High polarization, endurance and retention in sub-5 nm Hf0.5Zr0.5O2 films

High polarization, endurance and retention in sub-5 nm Hf0.5Zr0.5O2 films

J. Lyu, T. Song, I. Fina, and F. Sánchez

Nanoscale 12, 11280 (2020)

DOI: 10.1039/D0NR02204G

Abstract

Ferroelectric HfO2 is a promising material for new memory devices, but significant improvement of its important properties is necessary for practical application. However, previous literature shows that a dilemma exists between polarization, endurance and retention. Since all these properties should be simultaneously high, overcoming this issue is of the highest relevance. Here, we demonstrate that high crystalline quality sub-5 nm Hf0.5Zr0.5O2 capacitors, integrated epitaxially with Si(001), present combined high polarization (2Pr of 27 μC cm−2 in the pristine state), endurance (2Pr > 6 μC cm−2 after 1011 cycles) and retention (2Pr > 12 μC cm−2 extrapolated at 10 years) using the same poling conditions (2.5 V). This achievement is demonstrated in films thinner than 5 nm, thus opening bright possibilities in ferroelectric tunnel junctions and other devices.

 

Unraveling Ferroelectric Polarization and Ionic Contributions to Electroresistance in Epitaxial Hf0.5Zr0.5O2 Tunnel Junctions

M. Cervo Sulzbach, S. Estandía, X. Long, J. Lyu, N. Dix, J. Gàzquez, M. F. Chisholm, F. Sánchez, I. Fina,* and J. Fontcuberta*

Adv. Electron. Mater. 2019, 1900852

DOI: 10.1002/aelm.201900852

Abstract

Tunnel devices based on ferroelectric Hf0.5Zr0.5O2 (HZO) barriers hold great promises for emerging data storage and computing technologies. The resistance state of the device can be changed through use of a suitable writing voltage. However, the microscopic mechanisms leading to the resistance change are an intricate interplay between ferroelectric polarization controlled barrier properties and defect‐related transport mechanisms. The fundamental role of the microstructure of HZO films determining the balance between those contributions is demonstrated. The HZO film presents coherent or incoherent grain boundaries, associated to the coexistance of monoclinic and orthorhombic phases, which are dictated by the mismatch with the substrates for epitaxial growth. These grain boundaries are the toggle that allows to obtain either large (up to ≈450%) and fully reversible genuine polarization controlled electroresistance when only the orthorhombic phase is present or an irreversible and extremely large (≈103–105%) electroresistance when both phases coexist.